I see this is an old thread, however I feel the need to introject being an engineer.

I expect the desire to pluralize stems from the fact that we are often working with multiple fractions at a time (eg 3/4), however we would be less inclined to want to pluralize 1/4. However the numerator is not the subject of this conversation, it is the unit of that number we are discussing. Strictly speaking I would also never encourage a student to pluralize any measurement as the unit is just that; one unit.

To elaborate 1/3 of two inches would actually be 2/3, which is clearly not the intention being communicated. I do agree with Ursus however, in any practical environment (and any guidelines) the deprecated sizes of late British royalty's body parts should no longer be used as units of measure in a competitive global environment.

Regarding fractions and decimal numbers, neither one is fundamentally more or less accurate than the other. Also, any number that can be represented by one can be represented by the other. Every single rational number, terminating or repeating, can be represented as a fraction.

Irrational numbers, non-terminating and non-repeating, cannot be represented by a fraction OR a decimal number with perfect accuracy. They can only be approximated by such, and since every decimal can be converted to a fraction, any decimal approximation would be no more or less accurate than the corresponding fraction. Besides, while there are certain common conventions, accuracy can really only be known if the tolerance is specified for either.

Next, there's nothing special about inches that require the use of fractions whose denominator is a power of two. You can use English units but still use the decimal system for them.

in our company, we have our own style guide. the only individual number that is treated as singular is exactly one, neither more nor less. hence it should be "0.5 inches." but you can also write it as "half of an inch."

quote://Tolken says:June 9, 2008, 8:06amA. Inches are not subdivided as decimals, but as simple fractions. (That's why they're so accurate)//

how can fraction be accurate??? only if the value is exactly 1/2, 1/4 etc there are some numbers that can not be expressed with fraction, but can be written as accurate as you want with decimal system.For example square root of 2 cm (1.41421356....), can be written 14142 um and can be easily converted 141 mm, depending on accuracy one needs. How do you do that in inches?also metric system allows you to do random mathematical operations with random numbers without any converting.

im not saying you can not be more accurate using inches, you can, but it's useless as it is limited to only few numbers.

Yeah, really. I used to feel comfortable with things like "0.5 inches" and then for whatever reason I started saying "0.5 inch." I guess it's kinda like how I started to like hot peppers at some point in my up-bringing. Just a change of taste/habit.

You probably finished editing your technical manual a long time ago. At any rate, my personal experience tells me that "0.5 inch" may or may not be more correct, but at least sounds more technical. Maybe that's just because I started saying it later in my life, so I mark "0.5 inches" as more child-like and "0.5 inch" as more mature.

A. Inches are not subdivided as decimals, but as simple fractions. (That's why they're so accurate)

B. If something sounds wrong when you say it, then it is wrong, but maybe not for the reason you think. 0.5 inch is just as wrong as 0.5 inches AND "half an inch" (though this last is allowed as idiom). The only meaningful way of stating this measure is "half of an inch", hence "0.5 of an inch" which can probably be safely abbreviated to "0.5 in", horrible though the thought may be (see A above).

Alright, why?

We like the sound of 0.5 inches because "five" is plural. We're conditioned to use plurals with plural numbers from when we first start to speak, so in everyday speech it's very hard to overcome (and probably pointless to try). "0.5" is a means of expressing "five tenths" in mathematical notation. Five tenths are of course plural for tenths, but not for decimal fractions of one... however grammar does not legislate for number less than singular. For this reason alone, I was taught at school that "0.5 inches" was NOT WRONG, but might occasionally be pounced on by editors, and the only way to pass under the radar was to say "0.5 of an inch".